Project Summary/Abstract Bilingual children are at particular risk for being misdiagnosed with language impairment, a developmental disorder impacting language production and comprehension. This is due, in part, to the relative lack of clinically-appropriate tools for this population?many approaches that help identify language impairment in monolingual children can over- and underestimate language abilities in bilingual peers. One promising approach is to test word learning skills: monolingual and bilingual children alike have been found to have weaknesses in word learning relative to typically-developing peers. However, we do not yet know how bilingual children make use of information from both of their languages while learning words in each. Available research in adult bilingualism indicates that both languages are at play even when the speaker intends to use only one. To illustrate, adult bilinguals are more successful in learning new words in one language if they resemble words in the other (e.g., learning costa in Spanish is easier after learning coast in English). These findings have shaped models of adult bilingual language processing, which emphasize the potential for such cross- language interactions. Data also suggests that these cross-language effects (in adults) are linked with individual differences in inhibitory control, a cognitive function that helps individuals manage similar and competing information. In child bilinguals, neither the effects of cross-language similarity, nor their association with inhibitory control, have been fully explored. In bilinguals with language impairment, such work is virtually nonexistent. Addressing this gap, this work will test how Spanish-English bilingual preschoolers with language impairment and those with typical language development learn new words in each language. Critically, we will manipulate the similarity of these new words (in sound and meaning) across Spanish and English to test whether this facilitates learning in each group. Our approach includes measuring word learning outcomes with accuracy, response times and eye gaze during a comprehension task following exposure to the novel words. Enhancing the clinical relevance of this work, we will also investigate whether explicit instruction in cross- language similarities improves word learning. Finally, we add depth to these studies by assessing inhibitory control and testing for associations between language performance and this broader cognitive function. This work bears directly on clinical topics. If, as predicted, bilingual children with language impairment show weaker skills in drawing associations across languages, then cross-language effects may inform assessment of language skills in bilinguals. If the two groups perform similarly, particularly with explicit instruction, then this work informs an approach to treatment that may support development in each language concurrently. Overall, this work will refine the profile of language impairment with regard to bilingualism, addressing a well-known challenge in speech-language pathology. Finally, this work allows us to evaluate models of bilingual language processing?largely informed by data from adult bilinguals?in the context of language development.